Assistant Professor of Cardiology, Cardiovascular Research Committee, Jomhuri Islami Blvd., Kerman, Iran
Background- An elevated arterial pressure is probably the most important public health problem in developed countries. Although the measurement of blood pressure in the clinic has been the cornerstone of the diagnosis and management of hypertension, it has some limitations. Ambulatory blood pressure monitoring (ABPM) is a method of blood pressure assessment which compensates for some of the limitations and errors of clinical values such as the white coat phenomenon. Methods- In this cross sectional study, we enrolled 42 (20 male, 22 female) hypertensive patients who were under treatment. Each patient s BP was measured in clinic twice at 5minute intervals. ABPM having been set up, each patient s blood pressure was measured at 30- minute intervals during the day and 60- minute intervals during the night. The patients were advised to do regular daytime activities and record unusual activities. Results- The mean clinic BP 137.95±14.28/88.66±9.53 (mmHg) compared with a mean awake ambulatory BP (ABP) of 132.90±12.27/80.51±7.39 (mmHg). A white coat effect (Clinic-Ambulatory BP > 20/15mmHg) was present in 33.3% (19.15%-47.55%, CI 95%) of the individuals. The correlation coefficient of systolic pressure, diastolic pressure and heart rate between clinic and awake ambulatory measurements was 0.55, 0.48 and 0.57, which indicated a linear relationship (P<0.001). Multiple regression models showed that age, gender, occupation and the duration of hypertension (by year) after diagnosis have no significant effects on estimating awake ABP by clinical measurements but could lead to a better estimation.
Conclusion- The frequent occurrence of white coat phenomenon in these patients suggests that clinic BP assessment may not always represent usual awake ambulatory BP in patients receiving antihypertensive therapy. We also suggest that physicians who do not have the availability of ABPM use this model to estimate average awake BP by clinic BP measurements: awake systolic BP (mmHg)=0.52 x clinic systolic BP + 66; awake diastolic BP (mmHg) = 0.46 x clinic diastolic BP + 42; and awake heart rate (p/min) _ 0.33 x clinic heart rate + 52(Iranian Heart Journal 2003; 4 (4):25-30).